The present invention relates to a communication device which determines communication parameters depending on the situation and performs communication via a predetermined transmission channel using the determined communication parameters.
Upon communication between a plurality of communication devices, one communication device is able to generate a fixed or variable length communication frame, store some or all of data as an object to be transmitted in a payload of the communication frame, and transmit sequential data to a transmission channel on a communication frame basis.
The characteristics of the transmission channel via which the data is transmitted are inconstant and sequentially changed with environmental variation or the lapse of time. Various types of noise appear since various types of electric equipment are connected to a power line when the transmission channel is the power line. Impedance is changed with an alternating-current power waveform (AC waveform) and the characteristics of the transmission channel are changed.
Specifically, when a power line communication device which performs communication using a power line transmits a power line communication signal (hereinafter, also referred to as a PLC signal) to the power line as shown in the example of FIG. 24, the amplitude or waveform of the PLC signal is changed in response to the characteristics of the power line. This change is usually generated with the change of impedance (Z) (hereinafter, also referred to as the Z change) related to the power line. Usually, the Z change is periodically generated in synchronization with an alternating-current power waveform (AC waveform) as shown in FIG. 24.
In the example shown in FIG. 24, the impedance is changed at each of times t11, t12, t13, and t14 in the binary form. The Z change timing is generated in the vicinity of peaks and troughs of the alternating-current power waveform.
In FIG. 24, a PLC signal frame F11 is affected by the Z change since the Z change appears on a power line 700 from a time before time t11 to a time after time t12. Communication parameters of a frame subsequent to an FC (frame control section: corresponding to a header) are controlled in response to the impedance of an FC transmission period. Therefore, a transmission error does not occur since data packets appearing up to time t11 among a plurality of data packets included in a payload of the frame F11 have the same impedance as the FC, but data packets after time t11 all become error packets since the data packets after time t11 have the impedance different from the FC.
A frame F12 is also affected by the Z change. In this regard, pilot symbols (pilot signals) P1, P2, P3, P4, and P5 as known information are included in the middle of the frame F12. The influence of the Z change is less in the frame F12 than in the frame F11 since communication parameters of a signal subsequent to a pilot signal are controlled in response to the impedance of a transmission period of the pilot signal. However, data packets over the commencement (for example, t11) of the Z change or the termination (for example, t12) become error packets even in the frame F12 into which pilot symbols have been inserted.
A frame F13 is also affected by the Z change. Since communication parameters of a frame subsequent to an FC (frame control section: corresponding to a header) are controlled in response to the impedance of an FC transmission period, the communication parameters all become error parameters when the FC transmission period is over the commencement (for example, t11) of the Z change or the termination (for example, t12).
As a technique for reducing the influence of noise associated with an alternating-current power waveform, it is known that a zero-crossing point of the alternating-current power waveform is detected and data is transmitted in a sufficiently shorter period than a power supply cycle in the vicinity of the zero-crossing point.
Patent Literature
PTL 1 JP-A-59-143435